1. Field of the Invention
This invention relates generally to a method and apparatus for removing the accumulation of combustion ash and slag from the interior of a cyclone furnace and, more particularly, to a method and apparatus for deslagging a cyclone furnace by establishing vibrations in the furnace with controlled, sequential explosions.
2. Description of the Related Art Steam operated generators are used for producing electricity in electric power plants. Steam is produced by heating the external surfaces of panels of tubing. Commonly, heat is provided by the combustion of gas, oil, coal or other hydrocarbon fuels. Combustion of these fuels is incomplete, producing large amounts of waste material.
The controlled combustion of pulverized coal is a common fuel source. However, coal contains numerous impurities that are not efficiently burned and show up as waste material, such as fly ash and slag. This ash and slag collects on the interior surfaces of the cyclone furnaces used to burn the fuel.
In a typical coal fired steam operated generator, several cyclone furnaces are used. Pulverized coal is introduced into the furnace and is ignited in the firebox or combustion chamber. The walls of the cyclone furnace include a number of tubes, and the combustion of the pulverized coal heats water in the tubes to form steam, which is then introduced to a steam turbine.
As discussed above, incomplete combustion of coal produces ash and slag that accumulates in the cyclone furnace. As molten fuel cools, the ash and slag accumulates on the interior surfaces of the combustion chamber. Although it is possible to limit the accumulation of ash and slag by using coal with a heavy pig iron content, environmental concerns make this type of coal undesirable, in many instances, because of its heavy metal content. With other types of coal, the impurities, including dirt and clay, result in large amounts of ash and slag, and these impurities collect on the bottom and sides of the cyclone furnace.
Typically, a steam-operated generator will have as many as 12 to 16 cyclone furnace units. A typical cyclone furnace 10 is shown in FIG. 1. The fire box or combustion chamber 20 of the furnace has a diameter anywhere from approximately 4 feet to 12 feet. In that combustion chamber, there are generally included at least two air inlets, as well as gas inlets, oil inlets, coal inlets, etc. to enable the input of fuel. The pulverized coal and other fuel swirls around during the combustion process in the combustion chamber. Ideally, molten slag exits the combustion chamber by the slag tap hole 23 shown in FIG. 1 and collects in a slag tank for disposal. However, when there are heavy accumulations of ash and slag due to impurities in the coal, there is a collected residue of ash and slag at the bottom of the furnace.
The slag and ash accumulated in the cyclone furnace may be as thick as 12 to 18 inches at the bottom of the combustion chamber, and approximately 2 inches thick at the top and sides. As shown, the fire box or combustion chamber is generally a cylindrical shaped chamber. The slag or ash that accumulates is very smooth, dense and hard.
As shown in FIG. 2, tubes around the combustion chamber of the cyclone furnace are used to heat water that is then delivered to a steam turbine. The ash and slag buildup in the combustion chamber reduces the overall efficiency of the generator by requiring additional combustion and fuel to properly heat the water within the tubes. In fact, when the slag buildup has occurred, the thermal efficiency of the plant is reduced substantially.
In the past, it is a common practice to periodically clean out the ash and slag from the combustion chamber of cyclone furnaces. This cleaning process normally involves extensive washing with a high pressure water solution, commonly referred to as hydroblasting. Hydroblasting involves inherent problems such as requiring a complete shutdown of the facility for approximately the 12 to 24 hours needed to hydroblast out several cubic yards of accumulated slag and ash. With the typical number of 12 to 16 cyclone furnace units in a plant, well over a million gallons of water are needed to hydroblast out the accumulated slag and ash. This time to hydroblast out the buildup results in lost revenue to the plant because of the down time. The combination of water and ash produces a concrete like material which, if allowed to dry, would harden like concrete and further exacerbate the cleanup problem. In addition, a hydroblasting operation requires the use of expensive wet ash handling equipment, as well as the extensive manpower required to operate it.
An additional byproduct of a hydroblasting operation is the production of sulphuric acid. The water combines with the sulphur oxide in the fly ash, particularly with sulphur laden coal, to produce an acid that is highly corrosive. Thus, immediate attention must be given to the dilution or removal of the sulphur acid to prevent undesirable corrosion and repair of the facility.
The present invention is directed to overcoming one or more of the problems set forth above.